Unfortunately one very popular brand Heat Detector at the time made in1980s thru 90s and by the thousands by Chemetronics Inc. has a very dangerous flaw to it where it allows the terminals where wiring is attached to pop off its mounting base and then no protection is the result often time the Fire Alarm Panel is not even made aware of the dangerous condition. as the circuit is not broken to allow a trouble condition at panel.
in this case was causing a false alarm every time a train came by this factory on Neville Island Pa. and vibrated the brass connection against the steel beam .
Part of the problem also is these where private labeled and sold under many different names . Chemetronics is no longer in business and may have been bought out.
Needless to say every one of these units will be changed in this plant ,but there are thousands more out there with this same potential and when called on will not cause an alarm condition.
I notified the Consumer Products Safety Commission about these units almost 20 years ago . and not only are these units still out there thousands of an earlier version of Chemetronics heat detectors where recalled back in mid 90s and I am still finding them on jobs and removing them took 2 out last year.
But this is not the only problem there are many smoke detectors and smoke alarms on recall as well siting in homes and business still being used as well.